Manufacture of electrical rectifiers



P 1940- P. H. DQWLING 2,213,389 I MANUFACTURE OF ELECTRICAL RECTIFiERS Filed March 19, 1958 lNV ENTOR Philzp fLDowk'ng.

HIS ATTCRNEY v Patented Sept. 3, 1940 PATENT OFFICE MANUFACTURE OF'ELECTRICAL RECTIFIERS Philip H. Bowling, Forest Hills, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application March 19, 1938, Serial No.-196,9 11

19 Claims; (01. 17 5-366) My invention relates to the manufacture of electrical rectifiers, and particularlyto the manufacture of rectifier elements for copper oxide rectifiers.

5 One object of my invention is to improve the rectifying characteristics of the rectifier elements.

Other objects and characteristic features of my invention will appear as the description pro- 10 ceeds.

I shall describe one process of manufacture embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a view 16 showing in elevation one form of blank ready to be prepared as a rectifier element in accordance with one process of manufacture embodying my invention. Fig. 2 is a view showing a number of blanks assembled on a support as they appear go during one step in the process of manufacture. Fig. 3 is a vertical sectional view showing, in an exaggerated form, a rectifier element as it appears nr another step in the processof manufacture embodying my invention. Fig. 4 is a 25 view showing a completed rectifier element, constructed in accordance with my invention.

Similar reference characters refer to similar parts in all four views.

In the process of manufacturing copper oxide rectifier elements, as it is now generally prac tlced, a. number of copper blanks which may, for example, be similar to the blank A shown in Fig. l are first cleaned, usually by subjecting them to the action of a strong solvent for copper, and then 5 rinsing-them in running tap water, that is, in water drawn from the city mains or other usual Water supply.- Any suitable solvent may be used, but a 50 per cent solution by volume of chemically pure nitric acid has been found to be particuo larly effective for this Purpo e. when a 50 per cent solution is used, the blanks should' preferably be immersed for at least 30 seconds. "The blanks "are then assembled in pairs on a suitable support or rack B in the manner 5 shown, in Fig. 2 so that have their adjacent faces A in contact. The blanks are then heated in the presence of' air in'an electric furnace, the temperature of v whichis usuallymaintained at about 1860". F. 50 This heating of the blanks causes a layer of r'ed or cuprous. oxide to be formed -on the blanks, and

- iscontinueduntil the cuprous oxide layer' is of the desired thickness. 'After a sufficient amount of oxide has been formed on the copper blanks, hese 56 blanks are then, transferred immediately a the blanks of eachsecond furnace which is maintained at a tempeiature of approximately 1050 F., and are allowed to remain in this latter furnace for at least a sufficient length of time to permit them to cool down to the temperature of the second furnace. The oxidized blanks are then removed from the second furnace and are suddenly cooled or quenched by plunging the blanks into cold water. Each blank then appears as shown in Fig. 3, from which it will be seen that each blank A is now covered with an inner coating D of cuprous or red oxide of copper and a thin outercoating C of black oxide of copper. It will also be seen from I an inspection of Fig. 3 that the flat face of the blank which is exposed during 'the oxidizing l5 process, that is to say,the lower face has a much heavier oxide coating than the upper face. Each blank is next treated to remove the black oxide from the lower face of the blank, and both the black and red oxide from the upper face, after which the blank will appear as shown in Fig. 4. One process which is particularly suitable for removing the excess oxide from the blanks is described and claimed in Letters Patent of the United States No. 2,094,642, granted to me on 5 October 5, 1937. As a last step, the electrical contact to the exposed face of the cuprous oxide remaining on the blanks is improved as by rubbing into this face powdered petroleum coke. Rectifier elements of the type described exhibit the characteristic of offering a relatively low resistance to current flowing through the elements from the cuprous oxide to the copper and a relatively high resistance to the flow of current through the elements in the opposite direction. 3! The resistance of, the elements in the low re-' sistance direction will hereinafter be referred to as the conducting resistance, while the resistance of the elements in the high resistance direction will hereinafter be referred to as the blocking resistance. v

Rectifier'elements of the type described also exhibit the characteristic that when a. voltage is applied to them in the highresistance or blocking direction, the high or blocking resistance will 4 decrease at first relatively rapidly and then somewhat more slowly with time until it attains an apparently stable value which'may be'considerably 1 less than the initial value. The stable virtual value of the reverse currentwhen an alternating n voltage is applied to the rectifier is increased due to this effect, and this effect accordingly in some ,instances' determines the voltage for which the rectifieris capable of effecting satisfactory rectification in service. This change in blocking re- 5 character, the apparent resistance in the reverse" sistance with time is ordinarily known as creep, or "reverse creep, and is usually temporary in directiori gradually returning toward its original value when the voltage is removed.

Rectifier elements of the type described further exhibit the characteristic that as time goes on i the resistance of the rectifier in the low resistance or conducting direction gradually increases.

' tude of the creep, but has a beneficial eflect onthe initial resistance and aging of the rectiflers in the conducting direction. These impurities may reach the oxidizing furnace from a number of sources. For example, they may accumulate on the copper blanks from exposure prior to being placed in the furnace, or they may be left i on the blanks by reagents or by the use of impure rinsing water in the precleaning operation, I

'or they may be present in. the form of dissolved gases, or they may be introduced into the fur- .nace on the forks or racks used to support the distilledwater immediately after they have been rinsed in tap water following the acid bath, and its purpose is-to remove from the blanks all impurities which may be left on them following the tap water rinse. ,In some instances, the re-- moval of the impurities can be facilitated by boiling the distilled water or maintaining it at the boiling point. .The time the blanks are left in the distilled water is not critical, but it is desirable to leave them-in the water for at least 3 minutes. This step canbe utilized in..co'nnection with the hereinbefore described process without the addition of the other steps to be described hereinafter, and its effects in most instances appear to be to cause the elements to havea somewhat higher resistance in both directions than would otherwise be obtained, and also to reduce the tendency to creep. These effects are not radicahand, while the initial resistance values in the high resistance directio will be rather uniform, the magnitude of the creep will be somewhat erratic. This. erratic behavior as regards creep depends to a certain .extent, at least, upon small variations in the orig- I inal metallic impurities which are present in the copper from which the blanks are formed, and can be eliminated' and the magnitude of the creep much reduced by the use of copper containing a small amount of lead as described in my copending application for Letters Patent of the United States, Serial No. 196,912, filed by me on March 19, 1938, for Electrical rectiflers.

The second additional step which may be impurities in the tap water subsequently remain accordance with my present invention, theseimbut, for many other applications, a small value next describe are calculated to introduce anodic one of its constituent atoms) will be taken up by and one way which has been found suitable to inappear to be. critical, and a solution saturated a added to the hereinbefore described process for .controlling the anbdic impurities consists in treating the supports on which the blanks are mounted while they are being oxidized just prior to mounting the'blanks on the supports to re- 5 move any impurities which may be present on the supports. This treatment is generally necessitated by the fact that the quenching of the blanks of each charge following their oxidation is usually effected by immersing the blanks while 10 'still assembled on the supports in tap water, with the result that any impurities which maybe deposited on the supports due to the presence of on the supports when they are next used to effect the oxidation ofa new charge of elements. In

purities are removed either by thoroughly washing the supports in distilled water, or by raising them to the temperature (or higher) at which 20 the oxidation of the blanks is to be carried out, and then allowing the supports to dry or cool in clean air, as the case may be. Whenthe lastmentioned method of cleaning the supports is used, it is preferable to retain the supports at the oxidation temperature .at least as long as is normally required to oxidize the blanks.-

The addition of this and the previously described step to the hereinbefore described process yields rectifiers whose initial resistances in both directions are considerably higher than those of rectifiers produced by older methods. Furthermore, the magnitude of creep is very low and very uniform, and is more or less independent of small variations in the original metallic impuritiesin the copper blanks. For some applications of rectiflers, the increase in the value of the resistance in the conducting direction which these additional steps produce is not desirable,

of resistance in the conducting direction is sec-. ondary to an ability to maintain a high resistance value in' the high resistance direction, and, for such applications, the hereinbefore described process modified by the addition of the two steps just describedis particularly well suited. As will readily be seen from the foregoing description, the two steps Just described are calculated to remove from the blanks and racks, respectively, all impurities. The steps which I shall impurities into the process of manufacture in controlled amounts. Tests made with a large number. of foreign materials indicate that, ingeneral, any anion introduced into the process, or the copper, in such a way that this anion- (or the copper oxide, will produce the effects mentioned hereinbefore. Some anions which have been successfully-used are chlorine, carbon dioxide, iodine and the sulphate radical. However, I prefer to use either carbon dioxide or chlorine,

troducethese' anions ,into the process consistsin dipping the elements, or the supports on which the elements are mounted, or both, into a solution of distilled water containing carbon dioxid or chlorine following the thorough cleaning 0 these elementsin the-manner described herein before. The concentration of carbon dioxidei the solution when carbon dioxide is used does no atmospheric pressure is satisfactory. However, i desired, the concentration of the carbon dloxid may be increased by supersaturating the wa or by using the water under a high carbon dioxide pressureand at a low temperature. The chlorine content of the distilled water when ch rine is used may vary between a few parts, to per.-

haps one hundred parts per million by weight.

- In special cases where creep in the high resistsuch a way as to be taken up by the copper oxide,

in general, the opposite eifects to those produced by anions may be expected. Thus the use of a salt, such as sodiumchloride or sodium cyanide, produces a combination efiect, and in some cases it may be'desirable to use suchoa salt in proper concentrations.

If the supports on which the elements are mounted do not come into contact with any contaminating substances throughout the manufacturing process, the desired amount of impurities may be added to the supports by quenching them with their load of oxidized blanks in water containing the desired anion, thus eliminating the necessity for any special treatment of the supports.

It should be particularly pointed out that the steps which I have described need not necessarily all be used together, but that any combination of these steps may be employed to efiect any particular desired result It should also be pointed out that the characteristics of the rectifiers obtainediby the process.

of the fact that the amount of impurities present in the process are controlled, rectifiers having a high degree of uniformity are obtained.

Itshould also be pointed out that rectifiers manufactured in accordance with the process embodying my invention can be further improved by employing blanks containing lead in small concentrations,-and that such rectifiers are superior as regards stability in the high resistance direction to rectifiers produced in the absence, or

near absence, of all impurities in or on the blanks or racks or in the furnace during the oxidizing process. It should further be noted that the presence of the cathodic impurity lead in the copper sacrifices very little as regards the rectifylng characteristics of the elements in the low resistance direction, at least at voltages at which the rectifiers'are. usually used, over what can be obtained by the incorporation into the process 5 of a controlled amount of an anodic impurity. AlthoughI have herein shown and described only one process of manufacture of electrical rectiflers embodying my invention, is understood 'rinsing the blank in tap water to remove all traces of the acid, rinsing the blank in distilled water to remove all7impurities adhering to the blank from the tap water, and then heat treating said blank to form an oxide layer thereon.

2. The process of preparing a copper oxide rectifier element from a copper blank which consists in treating the copper blank to remove all surface impurities, dipping the blank in a solution of mospheric pressure with carbon dioxide, and then heat treating said blank to oxidize-it.

"4. The process of preparing a copper oxide rectifier element from a copper blank which consists in treating the copper blank to remove all.

surface impurities, subjecting the blank to a solution of distilled water containing carbon dioxide in small concentration, and then heat treating said blank to oxidize it. 5. The process of forming a copper oxide rectiher which consists in adding an anion to a copper body containing lead, and then heat treating said body to oxidize it.

5 6. The process of preparing a copper oxide rectifier element from a copper blank which consists in treating the copper blank to remove all surface impurities, subjecting the blank to a solution of distilled watercontaining chlorine insmall concentrations, and then heat treating said blank to oxidize it. k

7. The process of preparing a copper oxide rectifier element from a copper blank which consists in treating the copper blank to remove all surface impurities, subjectingthe blank to a solution -of distilled water containing a sulphate radical in small concentrations, and then heat treating said blank to oxidize it. J

'8. The process of preparinga copper oxide rectifier element from a copper blank which con-' sists in treating the copper blank to remove all surface impurities, subjecting the blank tofia solution of distilled water containing chlorine in any amount between a few parts and one hundred parts per million by weight, and then heat treating said blank to oxidize. it.

9. In the process of preparing rectifier elements from copper blanks in which the blanks are oxidized by mounting them on a support in an oxidizing atmosphere, thestep which consists in baking the support at the oxidizing temperature to remove all surface impurities'immediately before mounting the blanks on the 'support, 7, f j

10. In the process of preparing rectifier elements in which a copper blank is mounted on a support in an oxidizing atmosphere, the steps which consist in removing all impurities from the blank and the support just prior tomounting the blank on the support and subsequently adding to both the blank and the, support an anion.

11. In the process of preparing a rectifier element'from a copper blank which consists in cleaning the blank, assembling it on a support and-subjecting itto an oxidizing atmosphere, and then quenching the support and blank in tap water, the step which consists in washing the support in distilled water prior to assembling the blank on it, to remove impurities adhering to it] froma previous immersion'in tap water.

'12 In the process of preparing a rectifier element from a copper blank which consists in cleaning the blank, assembling it on a support and subjecting it to an oxidizing atmosphere, and

then quenching the support and blank in tap water, the step which consists in baking the support at the oxidizing temperature to remove all surface impurities immediately before mounting the blank on the support.

13. In the process of preparing a rectifier element'from a copper blank which consists in cleaning the blank, assembling it on a support and subjecting it to an oxidizing atmosphere, and then quenching the support and blank in tap water, the steps which consist in treating the support to remove all impurities adhering to it from a previous immersion in tap water and then immersing said support in a solution containing a known amount oi! an anion.

14. In the process of preparing rectifie elements from copper blanks in which the b anks are oxidized by placing them on a support in an oxidizing atmosphere, the steps just prior to oxidizing the blanks which consist in. treatinz.

both the blanks and the supports to remove all surface impurities. I

15. The process of forming a copper oxide rectifier which consists in treating a copper body.

containing lead to remove all surface impurities, adding to the body an anion by immersing the body in a solution of distilled water containing the anion, and then heat treating said body to oxidize it. i

16. The process of forming a copper oxide rectifier which consists in immersing 'a copper blank containing lead in a solution of nitric acid, immersing said blank in tap water to remove all traces oi the acid, rinsing said blank in a solution of distilled water containing an anion, and heat treating said blank to oxidize it.

1'7. The process of preparing a copper oxide rectifier element from a copper blank which consists in dipping the blank in a solution oi! distilled water containing carbon dioxide, and then heat treating said blank to oxidize it.

18. The process oi preparing a copper oxide rectifier element from a copper blank which consists in subjecting the blank to a solution of distilled water containing chlorine'in small concentrations. and then heat treating said blank to oxidize it.

19. The process or preparing a copper oxide v rectifier element iroma copper blank which consists in subjecting the blank to a solution of distilled water containing a sulphate radical in small concentrations. and then heat treating said blank to oxidize it.

PHILIP H. DowLmG. 

